First Years of Running for the LHCb Calorimeter S ystem. Sergey Filippov (Institute for Nuclear Research of RAS, Moscow) o n behalf of the LHCb collaboration. LHCb experiment. Purpose: CP violation and rare decays study. Main subsystems: - Vertex detector – Si strips
First Years of Running for the LHCb Calorimeter System
(Institute for Nuclear Research of RAS, Moscow)
on behalf of the LHCb collaboration
Purpose: CP violation and rare decays study
- Vertex detector – Si strips
- RICH1 – aerogel, C4F10
- Tracking stations – Si strips
- Warm magnet
- Inner tracker – Si
- Outer tracker – straw tubes
- RICH2 – CF4
- Calorimeter – ECAL, HCAL, preshower
- Muon stations – MWPC, GEM
- Single arm forward spectrometer: 1.9 < η < 4.9
- Impact parameter resolution 20 μm for Pt> 2 GeV/c
- dP/P from 0.4% at 5GeV/c to 0.6% at 100 GeV/c
- Invariant mass resolution: ~22 MeV/c2 for two-body B decays
JINST 3 S08005 (2008)
One layer of scintillator pads each.
~6 x 8 meters, 6016 x 2 channels.
Light collection with embedded WLS fibers.
Light yield ~25 ph.el. per MIP.
Segmentation: three zones
- Inner – pad size 40x40x15 mm3
- Middle – 60x60x15 mm3
- Outer – 120x120x15 mm3
SPD, PS and ECAL
Multi Anode PMT:
HAMAMATSU R760064 channels, 2x2 mm2
- Inner, Middle and Outer zones;
- Total of 3312 modules, 6016 cells;
Test beam data:
- Light yield: ~3000 ph.el./GeV
- Energy resolution:
Test beam data
- Iron/scintillator plates parallel to
the beam direction;
- The volume ratio Fe:Sc ~ 16:3;
- Instrumented depth: 1.2 m,
6 tile rows;
- ~5.6λi – used as a trigger device;
- PMT HAMAMATSU R-7899, same as for ECAL
- 2 zones;
- Inner (cells 13x13 cm2);
- Outer (26x26 cm2).
Total of 1488 cells, ~8.3x6.7 m2
- Large fluctuation of signals → maximal integration time within 25 ns slot;
- VFE board: two integrators per r/o channel alternating each 25 ns;
- 100 Front-End Boards (FEBs):
- Combines 64 ch SPD + 64 ch PS;
SPD: 1 bit signal (yes/no, 0.5 MIP thr)
PS: 10-bit ADC 40 MHz
– Parameters for pedestal subtraction, corrections for pile-up and gains;
– Digital pipe-line to store data until L0 decision
– Trigger block: production of data for L0 trigger.
- PMT signal clipping to eliminate atail beyond 25 ns;
- 192 Ecal + 54 HcalFEBs;
- FEB: 32 ch, same for ECAL and HCAL;
–12-bit ADC 40 MHz (80 pC full range);
– Pedestal subtraction;
– Digital pipe-line to store data until L0 decision;
– Trigger block: production of data for L0 trigger.
The calibration is performed using tracks pointing to a given cell.
The L0 trigger decision is based on Pt cut so the nominal sensitivity of ECAL cells is set depending on their (x,y) position: Emax(θ)=(7+10/sin(θ)) GeV.
The ECAL calibration was performed in several steps:
1. Pre-calibration before the startup of LHC. Based on PMT gain measurement with LED monitoring system; precision of ~8%. Overall cell-to-cell intercalibration precision ~13%.
Clear π0 signal was observed right after the LHC startup.
2. “Energy flow” method: for each cell the correction factor is derived from comparison of its average energy deposit per event to that in neighboring cells. Does not require high statistics (~1 M events), was performed shortly after the LHC startup. Precision of ~4-5%.
3. Fine calibration using position of the π0 peak.
4. E/p calibration with electrons.
For each cell distribution of the invariant mass of two photons is filled for γγ pairs with centre of one of γ’s cluster at this cell. The correction factor for a cell is determined from the deviation of fitted π0 mass from the PDG value. Only a subsample of clusters with low energy deposition in PS (<10 MeV) is used at this step. The procedure is iterative, 5-6 iterations. To calibrate all cells, ~100M events is needed.
Performed every month, that corresponds to ~200 pb-1 of data. Precision ~1-2%.
π0 decays with converted or non-converted photonsare used to find the absolute normalization scale (“β-factor”) for PS.The EM shower energy is calculated off-line as
Both α and β being dependent on the shower position and origin (e- or γ).
The correction is determined in ECAL + PS calibration by minimizing the π0 width.
Another method to monitor or correct the ECAL cell calibration is through electron E/p.
Electrons are identified by estimation of the momentum of the extrapolated tracks and energy of the matching clusters.
Used to monitor ageing with applying aging trend corrections every 40 pb-1.
Useful when statistics of π0is low for mass distribution method.
E/p for electrons in ECAL
E/p for hadrons in ECAL
after one month
LED monitoring system is used to control HCAL response during data taking.
___ electrons in ECAL
___ hadrons in ECAL
Performance on data: ~4% misidentification rate at 90% efficiency
Track – ECAL cluster matching
Photon/merged π0 separation.At high pT (>3 GeV/c) ECAL energy depositions of both γ’s from π0 decay merge into a single cluster. The separation is based on cluster shape different for single and merged photons.
Mass resolution for resolved π0– 8 MeV/c2, merged – 20 MeV/c2.
LHCb Detector Operation
TDR, 14TeV: L=2.x10³² cm⁻² s⁻¹ with average number of interactions per event μ = 0.4
2012, 8 TeV: L=4.x10³² cm⁻² s⁻¹ with μ<=1.8
Two sources of degradation:
- radiation demage of scintillator tiles and WLS fibers (~0.25 Mrad /year);
- PMT sensitivity loss.
0 mass variation as a function of time (luminosity) observed:
0 1 2 3 4 5
HCAL tile row
Light yield degradation in the HCAL centre
HCAL PMTs anode currents are 5 times more the for ECAL.
Integrated anode currents are up to 100C.
Gain reduction vs. integrated anode current was
studied in the lab.
Lost of sensitivity for ECAL/HCAL PMTs
Physics performance: Radiative decays
Measurement of the ratio of branching fractions B(B0→K∗0γ )/B(B0s→φγ)
Proceed through electromagnetic transitions b->sγ. Sensitive to extensions of SM.
Invariant-mass distributions of the (a) B0→ K∗0γ and (b) B0 →K∗0γ decay candidates.
Nucl. Phys. B 867 (2013) 1-18
Physics performance: B0s→J/ψη(‘)
The ratio of the branching fractions of B0s→J/ψηand B0s →J/ψη’ decays is measured to be
Invariant mass distributions for selected B0s→J/ψη(‘) candidates. The thin solid orange lines show the signal B0s contributions and the orange dot-dashed lines correspond to the B0 contributions.
Nucl. Phys. B 867 (2013) 547-566
LHCb calorimeter upgrade
In 2015-2017, LHCb is expected to take 5-7 fb-1 of data @13 TeV. There is strong physics case to continue the flavor physics programme. This requires running at higher luminosities: (1-2)·1033 @√s = 14 TeVafter 2018.
With the present trigger organization, 1 MHz L0 limit: for all the hadronic final states, no gain from increasing the luminosity.
A fully software trigger is necessary to select desired final states.
For LHCb calorimeter system
LHCb Upgrade LoI: CERN-LHCC-2011-001
LHCb Upgrade Framework TDR: CERN-LHCC-2012-007
LHCb Trigger Organization
Current: latency-buffer in FE, and zero-suppress after L0 trigger
Upgrade: zero-suppress in FE, no trigger decision to FE, LLT in back-end.
Yu. Guz CHEF 2013 LHCb Calorimeter Upgrade